OB question regarding effacement

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Hi nurses..
I am currently in OB and LOVE IT I'm a little confused STILL on effacement. I understand that 100% effacement means that the cervix is ripened and birth is right around the corner. And, in order to give birth, the woman must be dilated to 10cm. Vaginal birth. What confuses me is just Friday evening I had a 16 year old patient who was 90% effaced BUT ONLY dilated 1cm.
I thought that if you are 100% effaced, labor is right around the corner and therefore, you the patient would be dilated to about 8-10cm? Right?
How is this possible? I am soo confused.

Not necessarily. The opening of the cervix is dilation. The THINNING out of the cervix is effacement. It's not unheard of that you can be almost all thinned out and not very dilated. Many times what you see is that the cervix won't dilate a whole lot before it's pretty well effaced first. This is why it takes so long at the beginning of labor, especially with primips.

i've put together some links for you to explore. i think you will find the answer to your question in the first 2 or 3 links. there is a difference in the way effacement procedes in primiparas and multiparas. i threw in a link to the bishop score in case you wanted to see what it was. the slide show on normal and abnormal labor is from a medical school and may or may not be interesting to you. i also included the two interactive tutorials on vaginal birth and c-section from medline plus since you are studying ob. the trick to understanding ob like any other medical condition is to have a good foundation and understanding of what is normal. it's when things go wrong that the fun really starts, and in ob there's a lot of complications that can occur--a lot!

Not necessarily. The opening of the cervix is dilation. The THINNING out of the cervix is effacement. It's not unheard of that you can be almost all thinned out and not very dilated. Many times what you see is that the cervix won't dilate a whole lot before it's pretty well effaced first. This is why it takes so long at the beginning of labor, especially with primips.

OB is AWESOME. enjoy it!

Excellent information. When I was working OB, we would judge effacement (with sterile vaginal exams) by the length of our index finger to the middle (proximal) joint. Cervix all the way to the middle joint (about 2" thick) = 0% dilated. Cervical thickness now a little beyond first (distal) joint (about 1") = 50% dilated. Cervix now at the bottom of my fingernail (about 1/2") = 75% dilated. Cervix paper thin, can't feel any more: 100% effaced.

We judged dilation with this quick rule: fingertip (index finger): 1 cm; index finger able to be inserted, move just a little: 2 cm; tips of index and middle fingers, tight fit: 3 cm; tips of index and middle fingers, can move around just a little: 4 cm; when you can spread your index and middle fingers all the way and no longer feel any cervix at all = 10 cm (watch out!)

What awesome posts!! I just wanted to add, I had a multip come with a broken leg at 38 wks, observation until AM to set leg. She c/o wet panties, I nitrozined and did SVE, she was 100% effaced and less than one CM when I touched her cvx, it went from less than 1cm to 4cm just from me touching it. We had the baby in time for her to go down and have her leg set on schedule.

Generally, yes. In primips effacement starts and is often still going on when dilation starts. Effacement takes a lot longer with the first delivery. In multips effacement is often complete before dilation starts. If you read further into this you will find that assessing effacement is a factor that is looked at in premature births.